The present invention relates to an air intake system for an internal combustion engine, which is provided at an upstream side of an intake port and generates gas flow (or gas stream) such as tumble flow in a combustion chamber of the internal combustion engine using a valve body by changing a cross section area of a part of an air intake passage.
For instance, Japanese Patent Provisional Publications No. 2010-121551 (hereinafter is referred to as “JP2010-121551”) and No. 2010-242618 (hereinafter is referred to as “JP2010-242618”) each disclose an air intake system for the internal combustion engine, which is capable of changing an opening area of the air intake passage by a valve body whose rotation angle is changed from a fully open position in which a quantity of suction air flowing in the air intake passage becomes a maximum to a fully closed position in which the quantity of the suction air flowing in the air intake passage becomes a minimum.
This air intake system is configured so that the valve body, which has a valve portion that is offset in a radially outward direction with respect to a rotation axis of a supporting shaft of the valve body, is rotatably supported in the air intake passage that is formed inside a housing. Then, by rotation of the valve body, the cross section area of a part of the air intake passage can be changed.
In JP2010-121551 and JP2010-242618, to employ this configuration, a valve accommodating recess (a valve accommodating space) is formed on an inner wall surface at a vertically lower side in the air intake passage. More specifically, the valve accommodating space is formed so that when the valve body rotates and is positioned in the fully open position, the valve body can be fully accommodated in the valve accommodating space.